1. Field of the Invention
The present invention relates to a dissolved air floatation (DAF)-type pretreatment apparatus and, more particularly, to a DAF-type pretreatment apparatus capable of removing foreign objects (or foreign materials) such as floating matter, turbid matter (or turbidity solids), alga (or algae), and the like, contained in raw water such as saltwater, sewage, or waste water, and the like.
2. Background of the Invention
In general, in order to remove foreign materials such as floating materials, turbid matter, alga, and the like, contained in raw water such as saltwater, sewage, or waste water, and the like, a related art pretreatment apparatus employs a water treatment method including flocculation-precipitation-filtering processes, flocculation-floating-filtering processes, or the like.
Among the processes, in particular, the floating process is performed as follows.
For example, a related art floatation system includes a reaction tank, a flocculation tank, a floatation tank, a circulation pump, a saturator tank, an air compressor, and the like. Here, a stirrer is installed in the flocculation tank and the reaction tank, respectively, in order to mix foreign objects contained in raw water and a flocculant (or a coagulant) input to (or applied to) raw water to form flocks.
In another example, instead of the reaction tank and the flocculation tank having a stirrer, the related art floatation system may include a hydraulic reaction tank and a flocculation basic which do not require power, a floatation tank, a circulation pump, and the like.
However, in the case of the floatation systems of the two examples, processing capacity of the floatation tank is limited to a particular range, i.e., to a range of 10 to 25 m3/hr, and thus, a larger amount of floatation tanks are required in a large capacity pretreatment process. As a result, a size of the floatation system is required to be increased, and thus, a larger space for the installation of the floatation system is required to be secured.
Also, the related art floatation system is known to be effective to remove floatation material such as alga, or the like. However, since the related art floatation system is not effective to remove suspension solids, it is not used alone. Thus, the related art floatation system is required to perform a precipitation or separation process to remove suspension solids contained in produced treatment water. In the precipitation process, saltwater, sewage, waster water, and the like, is filtered through a gravitation method or a pressure method mainly by using particulate filtration materials such as gravel, sand, anthracite, and the like, but the related art floatation system cannot properly serve as a filter when a large amount of alga such as a red tide, or the like, flows in.
Thus, in order to prevent this, the related art floatation system additionally adopts a DAF process before the precipitation process, configuring a two-stage pretreatment facility. The two-stage pretreatment facility, however, requires an area of a site for a precipitation system to perform a precipitation process, which results in an increase in the cost of construction and operating expenses. In order to solve the problem, a pretreatment process incorporating the floatation process and a sand filtration process has been developed, but it is disadvantageous in that operation performance of the floatation process is limited by the sand filtration process.
In another example, a gravitation-type fiber filter, instead of the foregoing sand filtration process, is installed in a production processing water tank for the floatation process, combining the floatation process and the gravitation-type fiber filtering process into a single process. In this case, however, since the size of the production processing water tank should be increased to install a required amount of gravitation-type fiber filters, the area of a site is disadvantageously required as much.
In addition, the gravitation-type fiber filter has a problem in that when back washing is repeatedly performed, fibers may be easily broken due to a short-term fatigue load and may be entangled to restrain back washing from being properly performed. Also, when fibers of the gravitation-type fiber filter are broken or entangled, the gravitation-type fiber filter should be replaced by a new one frequently, increasing maintenance cost.